Was Justin Bieber's dad his partner in crime?

Sources familiar with the situation tell TMZ ... 38-year-old Jeremy Bieber was not only present when Justin was arrested early Thursday morning ... he was one of the people who helped block off the residential street so his son could drag race.

It's even worse ... Jeremy was in SET nightclub just before the arrest with Justin and was around him all day, when the self-confessed little pothead was smoking weed.

As TMZ reported ... Justin admitted that he was under the influence of Rx drugs, alcohol and weed at the time of his arrest ... and Justin's dad was right there in the mix.